Speed up CalledAsConstructor....

src/builtins.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 69 matching lines @@
 // NOTE: Argument 0 is the receiver. The first 'real' argument is
 // argument 1 - BUILTIN_ARG(1).
 #define BUILTIN_ARG(n) (__builtin_arg__(n, __argc__, __argv__))
 
 
 #define BUILTIN_END                             \
   return Heap::undefined_value();               \
 }
 
 
-// TODO(1238487): Get rid of this function that determines if the
-// builtin is called as a constructor. This may be a somewhat slow
-// operation due to the stack frame iteration.
 static inline bool CalledAsConstructor() {
+#ifdef DEBUG
+  // Calculate the result using a full stack frame iterator and check
+  // that the state of the stack is as we assume it to be in the
+  // code below.
   StackFrameIterator it;
   ASSERT(it.frame()->is_exit());
   it.Advance();
   StackFrame* frame = it.frame();
-  return frame->is_construct();
+  bool reference_result = frame->is_construct();
+#endif
+  Address fp = Top::c_entry_fp(Top::GetCurrentThread());
+  // Because we know fp points to an exit frame we can use the relevant
+  // part of ExitFrame::ComputeCallerState directly.
+  const int kCallerOffset = ExitFrameConstants::kCallerFPOffset;
+  Address caller_fp = Memory::Address_at(fp + kCallerOffset);
+  // This inlines the part of StackFrame::ComputeType that grabs the
+  // type of the current frame.  Note that StackFrame::ComputeType
+  // has been specialized for each architecture so if any one of them
+  // changes this code has to be changed as well.
+  const int kMarkerOffset = StandardFrameConstants::kMarkerOffset;
+  const Smi* kConstructMarker = Smi::FromInt(StackFrame::CONSTRUCT);
+  Object* marker = Memory::Object_at(caller_fp + kMarkerOffset);
+  bool result = (marker == kConstructMarker);
+  ASSERT_EQ(result, reference_result);
+  return result;
 }
 
-
 // ----------------------------------------------------------------------------
 
 
 Handle<Code> Builtins::GetCode(JavaScript id, bool* resolved) {
   Code* code = Builtins::builtin(Builtins::Illegal);
   *resolved = false;
 
   if (Top::context() != NULL) {
     Object* object = Top::builtins()->javascript_builtin(id);
     if (object->IsJSFunction()) {
@@ skipping 647 matching lines @@
       if (entry->contains(pc)) {
         return names_[i];
       }
     }
   }
   return NULL;
 }
 
 
 } }  // namespace v8::internal